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An employee at the gun shop where the former Guardsman allegedly bought the AR-15 said they cooperated with the FBI investigation. News4's Shomari Stone reports. (Published Tuesday, July 5, 2016)

A former National Guardsman from Virginia is being charged with plotting to help the Islamic State group and contemplating a Fort Hood-style attack against the U.S. military.

Mohamed Jalloh, 26, of Sterling, Virginia, made an initial appearance Tuesday in federal court in Alexandria.

Court records made public Tuesday said Jalloh is a former member of the Army National Guard who said he quit after hearing lectures from radical cleric Anwar al-Awlaki.

A court affidavit spelled out a three-month sting operation in which Jalloh said he was thinking about carrying out an attack similar to the 2009 shootings at Fort Hood, which left 13 people dead.

Jalloh, who is a naturalized U.S. citizen originally from Sierra Leone, spoke in April and May with someone he believed was an ISIS supporter, the affidavit said. That person was actually an FBI informant.

When discussing attack operations with the informant on May 1, Jalloh said he believed attacks were "100 percent the right thing," the documents said.

"Sometimes, you just have to take action. You can't be thinking too much. You have to pick a action and take it," Jalloh said in a recorded conversation, the affidavit said.

In an earlier meeting, on April 9, Jalloh told the informant he was considering conducting an attack like that of Maj. Nidal Hasan, who fatally shot 13 people and wounded 32 others at Fort Hood on Nov. 5, 2009, the documents said.

The informant asked him to clarify what he meant.

"Nidal Hasan type of things. That's the kind of stuff I started thinking, you know," Jalloh said on tape, the affidavit said.

Jalloh also praised the man who shot and killed five members of the military in Chattanooga, Tennessee, in July 2015, prosecutors said. The gunman was a "very good man," Jalloh said, the documents said.

He also gave $500 to a federal agent he believed was working with ISIS, the affidavit said.

Court records indicated the FBI saw Jalloh buying an assault rifle Saturday at a gun shop in Chantilly, Virginia. The affidavit is not clear as to whether authorities believe Jalloh planned to use the rifle himself or whether he may have been procuring it on behalf of an informant. He was arrested Sunday.

Jalloh's sister, Fatmatu Jalloh, said in a brief telephone interview that she is serving as one of her brother's attorneys. She said she had not yet seen the unsealed charges but denied he would be helping the Islamic State group.

Outside the federal courthouse on Tuesday, attorney Asraf Nubani, who also is representing Jalloh, declined comment.

Last month, the affidavit said Jalloh drove to the Charlotte, North Carolina, area with another person looking for weapons to buy.

On Friday, Jalloh tried to buy an AR-15 assault rifle from a Chantilly gun store but was turned away because he lacked the proper paperwork. The affidavit said he returned the next day and bought a different assault rifle, which was rendered inoperable before he left the store.

The FBI believes Jalloh first made contact with ISIS supporters in summer 2015 during a six-month trip to West Africa.